Voltage-Gated Ion Channels Voltage-dependent ion channels play a fundamental role in the generation and propagation of the nerve impulse and in cell homeostasis.

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Voltage-Gated Ion Channels Voltage-dependent ion channels play a fundamental role in the generation and propagation of the nerve impulse and in cell homeostasis. General architecture of voltage-gated channels (Na + and Ca 2+ ).The “+” or “-“ signs indicate charges that have been implicated in voltage sensing. Transmembrane segment (cylinder) Pore Voltage sensor part of the channel Lipid bilayer The voltage sensor is a region of the protein bearing charged amino acids that relocate upon changes in the membrane electric field. Segments (S5 and S6) and the pore loop were found to be responsible for ion conduction.

Voltage-Gated Ion Channels The Gate The ion conduction through the pore may be interrupted by closing a gate Comparison between a field-effect transistor (FET) and a voltage gated ion channel. The FET transistor is represented as a p-channel device to make a closer analogy to a cation selective voltage-gated channel. In the FET, D is the drain, S is the source, and G is the gate. Closed states Open states Lipid bilayer voltage gated ion channel field-effect transistor

Voltage-Gated Ion Channels Ionic and gating currents in Shaker-IR K + channel Time course of ionic currents for pulses to the indicated potentials starting and returning to –- 90 mV Time course of the gating currents for the pulses indicated. The voltage dependence of the open probability and the charge moved per channel.

Voltage-Gated Ion Channels Typical gating current trace Gating current recorded at 10-kHz bandwidth. When the bandwidth is increased to 200 kHz, the first surge of current is the predominant amplitude The time course of the charging of the membrane capacitance for the experiment in (b).

Voltage-Gated Ion Channels Current fluctuations in gating currents Top trace is the time course of a pulse to +10 mV; middle trace is the variance and bottom trace is the mean computed from several hundred traces. Top trace is the time course of a smaller pulse to - 40 mV; middle trace is the variance; lower trace is the mean computed from hundreds of traces.

Voltage-Gated Ion Channels Three models of the voltage sensor Helical screw modelPaddle model.Transporter model. Positively charged residues